This invention relates to screen printing in general, and more particularly to a roller squeegee for use in screen printing machines.
The invention also relates to screen printing machines having the novel roller squeegee.
The purpose of a roller squeegee in screen printing is to force the printing medium--ink, adhesives, foams, or any of the other substances which can be applied in this manner--through the openings of the screen (stencil). For this purpose the roller squeegee is located above a surface portion of the screen, which may be a flat screen or an endless (e.g. belt or drum type) screen. If the screen is of the endless type, the squeegee is located within the space surrounded by the screen. The workpiece to be printed, e.g. carpeting, rugs, textiles, or the like, is located beneath the screen and the roller squeegee rests on the screen; in fact, it is known in the case of endless printing screens to use magnets which actually draw the roller squeegee more firmly into contact with the screen, i.e. towards the workpiece. Since printing screens, especially those of the endless type, are very thin and would be easily deformed or otherwise damaged by the weight of the roller squeegee, the workpiece (and thus the screen) is supported from below by a counter roller, a worktable or a pressure beam. This prevents damage to the screen and, at the same time, assures uniform pressure of the squeegee roller via the screen on the workpiece.
From U.S. Pat. No. 4,106,407 (Mitter), which is incorporated herein in its entirety by reference, it is know to use a roller squeegee which can be pressed against the screen (and hence the workpiece) by internal fluid pressure to obtain uniform printing results over the entire width of the screen (i.e. length of the roller squeegee).
There are, however, circumstances--particularly certain types of workpiece materials--where the pressure exerted by the weight of the roller squeegee on the screen (and hence on the workpiece) is undesirable and can, in fact, be detrimental to good print quality. In such cases it is desirable that the squeegee contact the workpiece via the interposed screen as uniformly as possible over the entire screen width, but that it exert no pressure or substantially no pressure at all. This has not heretofore been possible.